Temporal patterns of C and N under shrub canopy in a loessial soil desert ecosystem

In deserts organic matter and nitrogen are limited due to the most obvious characteristics of plant cover scarcity and low productivity. In order to establish whether an area is undergoing a progressive, long-term decline in biodiversity and productivity, more and more attention is being paid to temporal dynamics of organic carbon and nitrogen in desert ecosystems. In this study, a follow-up was performed on the temporal dynamics of carbon and nitrogen in a loessial plain in the Negev Desert, Israel. Following the investigation of the dynamics of total organic carbon (TOC), dissolved organic carbon (DOC), total soluble nitrogen (TSN) and mineralizable nitrogen (N) in the soils at a 0-10 cm depth between May 1998 and October 1999, we concluded that in the Negev loessial soil ecosystem: (1) soils under the canopy of shrubs had significantly higher concentrations of organic carbon and nitrogen than the soils between shrubs with different temporal dynamics, and nitrogen levels governed mainly by soil moisture, (2) the differences in organic carbon and nitrogen levels between soils under Hammada scoparia and Zgophyllum dumosum were slight compared to those in soil under and between the shrubs, but the soil under the Z dumosum canopy had significantly higher levels, (3) soils under canopies had the highest TOC and DOC levels in autumn and the lowest in summer and (4) patterns of organic carbon and nitrogen were significantly different between years. (C) 2001 Elsevier Science Ltd. All rights reserved.